Method of manufacturing noninductive helical filaments



July 5, 1932- w. L. PARRoTT 1,855,442

METHOD OF MANUFACTURING NONINDUCTIVE HELICAL FILAMETS Filed Jan. 28, 1950 111 ;r 7 bi gli 11i glo- INVENTOR BY WL. PH

ATTORNEY VPatentedv July 5, 1932 UNITED STATES PATENT OFFICE WABLEY L. FARB-OTT, F EAST ORANGE, NEW JERSEY, ASSIGNOB T0 WESTINGHOUSE LAMP COMPANY, A' CORPORATION 0F PENNSYLVANIA METHOD QF MANUFACTURING NONINDUCTIVE HELICAL `FILALIENTS Application lcd January 28, 1980. Serial- No. 423,933.

This invention relates to electron discharge devices and particularly relates to ,electron discharge devices employing hot cathodes of the indirectly heated type and more particu 6 larlyrelates to the heater element of said This application is a continuation in part application of my copending application Serial No. 402,559 filed October 26, 1929, en-

titled Methodof manufacturing electrondischarge devices.

One ofthe objects of the present inventionis to provide a method of forming a noninductive twin coil helical filament.

Another object of this invention is to pro vide a method for producing a non-inductive heater element for an indirectly heated cathode; y

Other objects and advantages will become apparent as the invention is more fully disclosed.

In copending application Serial No. 402,559 above identified, are disclosed two types of electron discharge devices employing electron emitting cathodes of the 'indirectly heated type, which are known to the trade as the 227 and the 224 radio receiving tubes. essential for best resultstoemploy a heater element in the cathode electrode which is substantially non-inductive.

A suitable type of non-inductive' heater A element is also disclosed therein which is comprised substantially of `a refractory metal filament shaped in the form of a double helix the turns of eachof said helices lying substantially in the same circumferential plane and in respective parallel spaced relationship.

As disclosed in said copending application y the specific type of double helix set forth therein may be formed from a hairpin shaped filament of the desired or predetermined wire size, length and diameter to conform with the specifically desired electrical and physical operating characteristics. The loop portion of the hairpin is engaged in a slot in the end of a mandrel of the desired coil inside diameter and the two legs of the filament wound about the mandrel the desired number In each of these tubes it is highly" of turns in the desired parallel spaced relationship. The specific pitch to the turns and number of turns per' inch depends upon the particular type cathode sleeve member within which it is to be incorporated. In the winding of the coil the two legs of the filament are preferably maintained in relativel close parallel spaced relationship to eac other while maintaining each set of two wire -turns at a relatively larger parallel spacing.

This arrangement effectlvel gives almost a complete neutralization o the electrical fields about the wire and coil and produces .the accompanying drawing wherein;

Fig. 1 is a side elevational view of a simple device for forming the specific non-inductive coil type heater element ofthe present invention;

Fig. 2 is a top view looking down on the device; 7

Fig. 3 is a view taken along plane III-III in F 1g. 1;

Fig. 4 is a side elevational view of the device shown in Fig. 1;

Fig. 5 is an enlarged sectional view taken along plane V-V in Fig. 1;

Fig. 6 is an enlarged sectional view taken along plane VI-VI in Fig. 1;

a coil which has a relatively low hum l char- Fig. 7 is an enlarged view of the tip of the mandrel about which the coil type lilament is wound;

Fig. 8 is a reverse view of the same;

Fig. 9 i's an enlarged view of hairpin type filament; and A Fig. 10 is an enlarged viewofthe complete non-inductive coil type heater element.

'Referring to Fig. 1 the device for winding the non-inductive coil type filament illus-l trated in Fig.- 10, is comprised substantially of a cross head 1, supporting posts 2 and 3, a guide plate 4, a screw drlvmg element 5 which may be turned b means of thumb plate 6 in the end of w ich screw driving element is inserted a mandrel 7. l

Guide plate 4 is provided with a suitable opening 8 to receive mandrel 7 and is also provided with openings 9 and 10 on opposite sides of themandrel opening 8, to receive the legs 11 and 12 of the hairpin filament shown in Fig. 9. The relative spacing of openings 8, 9 and 10 being in accordance with the desired spacing of the convolutions of the finished coil.

The mandrel 7 is comprised substantially of a wire havin the desired diameter, stren h and rigidity, such as for example a moly denum wire, the tip end of which is grooved in accordance with the design indicated in Figs. 7 and 8, for the purpose of engaging the loo end 13 of the hairpin lilament shown in i 9, thus restraining the loop end of the ii ament from lateral displacement when the mandrel is revolved about its longitudinal axis.

A coil type heater element formed in accordance with the present invention is comprised substantially of twin helices lying in the same cylindrical lane, the respective turns of said helices ing in substantial parallel spaced relationship.

From an examination of the enlarged view shown in Fig. 10 it may be. noted that the turns of` the filament are substantially in spaced pairs and that each of the spaced twin turns belong to opposite. helices. This feature is highly deslrable for the purposes of the present invention, in that it provides for a substantial neutralization of the electric 4field in each wire due to the passage of an alternating electric current therethrough. This neutralization of electric elds within the heater element eliminates a source of undesirable electric discharges resulting in deleterious hum characteristics of a thermionic discharge device employing an indirectly heated cathode.

The method of obtaining mechanically this twin turn spacing of a helical coilis one ofvthe features of the present invention. It maybe noted in Fig. 1 that guide plate 4 has a cut away section 14 adjacent to mandrel o ening 8.

In ig. 2 it may be noted that one of the openings 9 and 10 through which extend lilament legs 11 and 12 of the hairpin filament, lies within this recessed portion. I have found that when mandrel 7 is revolved about its longitudinal axis the two legs of a hairpin lament, the apex of which is engaged in the end of the mandrel 7, tend to wind or arrange themselves in the form of twin helices about the mandrel, the individual two'legs of the filament arranged themselves in the twin turn' spaced relationshi shown herein. I obtain th1s twin turn para lel spac- 1ng ofthe double helix by providing means comdprlsmg shoulder 15 in guide plate 4 for gui -ing one le of the ament in closer spaced relations ip to the other free winding leg, than would normally be obtained.

This mechanical feature of the invention is more clearly set forth in Figs. 5 and 6 which show in enlarged cross sectional view the manner in which the shoulder 15 effects the spacing of the coil convolutions. Ordinarily as above noted,A when mandrel 7 is rotated about its longitudinal axis the legs 11 and 12 of a hairpin-filament, the apex of which is engaged in groove 16 in the end of the mandrel, would tend t0 adjust themselves in parallel convolutions about the` mandrel, the .spacing and the -number of turns per inch belng dependent upon the spaced relationship of the openings 9 and 10 to the mandrel and the number of turns per inch to the thread of the screw driving element 5. This condition would hold true as long as the openings 8, 9 and 10 in guide plate 4 lie in substantially the same horizontal lane.

By lowering the plane o one of the openings as by recessing the grid plate member in the manner shown in Figs. 1 and 2 the parallel spacing of the twin turns is changed and shoulder 15 then becomes a guiding member for spacing one of the convolutions of the coil to the other. This can be clearly seen in Figs. 5 and 6 of the attached drawing wherein the convolutions formed by filament leg 12, which .for the purpose ofthe present invention may be denoted as the free or unengaged convolution, is shown in position within the guided convolution 11, the drawing setting forth clearly how shoulder 15 serves to guide the convolutions into the desired spaced relationship. The height of the shoulder 15 and the distance from the mandrel being controlling factors. In Fig. 6 the reverse view is shown.

As a result of the practice of the present invention I am enabled to mechanically form a double helix coil, the terminals thereof extending from one end, and the convolutions lying substantially in the same circumferential plane, and in relative parallel spaced relationship with each other, and am also enabled toA arrange the respective convolutions of one of said helices in predetermined or desired close spaced relationship with the convolutionsy of the other helix.

Such a type coil is useful in the art as an electrically non-inductive coil, and may be particularlyemployed as a heater element in thermionically active hot cathodes of the indirectly heated type wherein it is specifically desired to eliminate deleterious electrical discharges caused by induced electrical currents in such a heater element when energized by the passage of an alternating current therethrough.

In accordance with this specific application of the present invention the double helix element is comprised of a tungsten filament of approximately 6.5 mil diameter, preferably of the non-sag type. At this diameter the length requisite to give a current consuming capacity or resistance at the required 2.5 volts operating voltage of a common type radio receivin tube known to the trade as 227 or 224 tu es, is about 23 millimeters. This length of filament is wound upon a mandre`l of about 25 mil diameter, ad]usting the spacin of the turns to give approximately 20 dou le turns or 40 single turns per inch. This spacing provides a heater element with this length filament having approximately 10 twin turns or 20 single turns each of the twin turns being spaced apart about 1 millimeter distance and each of the sets of twin turns about twice this distance. By proper adjustment of the filament diameter, length, mandrel size, and pitch of the coil convolutions, heater coils of any desired dimension and electrical characteristics may readily be obtained.

The coil thus prepared may be employed in accordance with the invention set forth in the parent application of the present invention above identified.

Having broadly and specifically set forth the nature and scope of the present invention it is apparent that there may be many modifications in the apparatus and method of formin the speciiic type of non-inductive coil t pe lament herein disclosed, but such modi cations and variations are contemplated as may fall within the scope of the followin cla1ms: f

What 1s claimed is:

1. The method of forming a twin helical filament which comprises winding the legs of a hairpin filament in arallel spaced relationship about a mandli'el of the desired diameter.

2. The method of formin a twin helical filament which comprises s aping a length of the filament in the form of a hairpin, engaglng the loop of the hairpin in the end of a man rel of the desired diameter, and wind- ,ing the two legs of the filament about the mandrel in the desiredparallel spaced relationsl'ilp.

3. e method of forming a double helical filament, the convolutions thereof lying in substantially the same axial plane and in parallel spaced relationship which comprises engaging the loop end of a hairpin filament in the end of a mandrel of the de-v sired diameter, and winding the two legs of the filament about the mandrel in the desired spaced relationship.

4. The method of forming a double helical coil the convolutions thereof lying in substantially the same plane and in parallel spaced relationship, which comprises supporting a pair of wires on opposite sides of a mandrel, and winding said wires in parallel spaced relationshi about said mandrel.

5. The method of orming a non-inductive double helical iilament the convolutions thereof lying in substantially the same plane and in parallel spaced relationship which comprises supporting a pair of wires on opposite sides of a mandrel, winding said wires about said mandrel in parallel spaced relationship, and guiding one of said wires in relative close relationship to the other.

6. The method of forming a non-inductive coil type filament which comprises shaping the filament into a hairpin, and winding the two legs of said hairpin about a mandrel in relative close spaced relationship maintaining a relatively greater spaced relationship.

between the twin convolutions.

7. The method of forming a non-inductive coil type filament which comprises engaging the apex of a hairpin filament in the end of a mandrel, winding the legs of said hairpin about `the mandrel in arallel spaced relationship, guiding one oi) said legs in relative close spaced relationshi to the other.

In testimony whereo I have hereunto subscribed my name this 24th day of January,

WARLEY L. PARROTT. 

